Hidden move can be spotted

I have started to play pvp a long time ago and what i noticed that, when i use the hidden move swashbucklers use, it really helps to boost my attacks, which i . But in pvp, when i use it, an enemy uses an attack that hits me when im actually HIDDEN . How is this possible this really isnt fair cause what do you think HIDDEN means They shouldnt be able to see you on the map either